Project summary Gram-negative bacteria have an outer membrane which provides nutrients and added protection for the cell. Additionally, the outer membrane contains proteins that enable pathogenic bacteria to evade host immune responses and cause a number of serious infectious diseases. Despite the importance of these outer membrane proteins (OMPs) for cell survival and virulence, little is known about how these proteins are folded and inserted into the outer membrane. In E. coli, a 200 kDa five component complex called the BAM complex mediates the biogenesis of these membrane proteins and it is my goal is to use functional assays and structural biology techniques (X-ray crystallography, electron microscopy) to characterize the role that each component of the BAM complex serves and how substrate OMPs are recognized. These studies will assist in revealing the mechanism for the biogenesis of OMPs in Gram-negative bacteria and will offer clues to the biogenesis of OMPs in eukaryotic mitochondria and chloroplasts.